﻿/*
 *   _____                                ______
 *  /_   /  ____  ____  ____  _________  / __/ /_
 *    / /  / __ \/ __ \/ __ \/ ___/ __ \/ /_/ __/
 *   / /__/ /_/ / / / / /_/ /\_ \/ /_/ / __/ /_
 *  /____/\____/_/ /_/\__  /____/\____/_/  \__/
 *                   /____/
 *
 * Authors:
 *   钟峰(Popeye Zhong) <zongsoft@gmail.com>
 *
 * Copyright (C) 2010-2020 Zongsoft Studio <http://www.zongsoft.com>
 *
 * This file is part of Zongsoft.Data library.
 *
 * The Zongsoft.Data is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3.0 of the License,
 * or (at your option) any later version.
 *
 * The Zongsoft.Data is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the Zongsoft.Data library. If not, see <http://www.gnu.org/licenses/>.
 */

using System;
using System.Collections.Generic;

namespace Zongsoft.Data.Common.Expressions
{
	public class AggregateStatementBuilder : IStatementBuilder<DataAggregateContext>
	{
		public IEnumerable<IStatementBase> Build(DataAggregateContext context)
		{
			var statement = new AggregateStatement(context.Entity);
			var argument = (IExpression)null;

			if(string.IsNullOrWhiteSpace(context.Aggregate.Name) || context.Aggregate.Name == "*")
				argument = Expression.Literal("*");
			else
				argument = statement.From(context.Aggregate.Name, context.Aliaser, null, out var property).CreateField(property);

			//添加返回的聚合函数成员
			statement.Select.Members.Add(AggregateExpression.Aggregate(context.Aggregate, argument));

			//生成条件子句
			statement.Where = statement.Where(context.Validate(), context.Aliaser);

			yield return statement;
		}
	}
}
